Letter by Letter Animation
You may achieve it adding a Copy Rotation Constraint to every single letter and setting an Empty as a target.


Set the separate origin point to every single letter and add an Empty.


Select a letter, go to the Constraints header, choose Copy Rotation and set an Empty as a target. Repeat the process with every other letter.


Change the pivot center type to Individual Origins. Select an Empty and rotate it. Every letter copies the rotation of an Empty now.


Of course you may add a rotation shapekey to the entire object, but as you can see below it may cause some letters' deformations so I don't recommend it.